Method and apparatus for rendering medical materials safe

ABSTRACT

Infectious medical materials are rendered harmless by heating heterogeneous medical materials having wet and dry portions with a radio-frequency electric field. The medical materials may be comminuted prior to heating. The medical materials are exposed to the radio-frequency electric field in order to heat the medical materials. The medical materials may include sorted medical or veterinary waste which after heat treatment may be recycled.

This application is a continuation of application Ser. No. 193,724 filedFeb. 9, 1994 now abandoned, which is a continuation of application Ser.No. 77,046 filed Jun. 15, 1993 now abandoned, which is a continuation ofapplication Ser. No. 07/549,576 filed Jul. 6, 1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method of disinfectingmedical materials and more particularly to a method and apparatus fordisinfecting medical materials by exposing the materials toradio-frequency waves. The term medical materials encompasses medicalwaste, veterinary waste, and medical products.

The problems with current medical waste handling methods, like theproblems of solid waste disposal in general, are becoming increasinglyacute. Solid waste is primarily disposed of by burning or by burial inlandfill. Both of the methods have severe disadvantages. Burning ofsolid waste liberates waste particles and fumes which contribute to acidrain and other pollution of the atmosphere. Burying the waste results inpossible leaks of toxic chemicals into the surrounding earth andcontamination of ground water supplies. Although increasing amounts ofsolid waste are being recycled, which alleviates the problems ofincineration and burial, presently available recycling methods do notprovide a complete solution to the disposal problem.

Waste disposal is of even more urgent concern when the waste comprisespossibly infectious medical waste. Such infectious medical waste is aby-product of veterinary and medical care. For example, regulatedmedical waste consists of: (1) cultures and stocks of infectious agentsand associated biological materials; (2) pathological wastes; (3) humanblood and blood products; (4) contaminated sharps, including needles,syringes, blades, scalpels, and broken glass; (5) animal waste; (6)isolation waste, including gloves and other disposable products used inthe care of patients with serious infections; and (7) unused sharps.These wastes can generally be divided between (a) general medical waste,including cultures and stocks of infectious agents, associatedbiologicals, pathological waste, and human blood and blood products; (b)veterinary waste, including animal waste; and (c) waste that ispredominately plastic, such as the contaminated and unused sharps andisolation waste. The predominately plastic waste also includes metal aswell. Hospitals typically segregate waste by types. Contaminated sharpsand isolation waste, however, are of special concern as they may carryhighly dangerous pathogens such as AIDS virus or hepatitis virus. Sharpsin particular have caused widespread public concern when observed washedup on beaches or in public areas.

Hospitals and other generators of medical and veterinary waste employthree methods of waste handling: (a) on-site incineration of the waste,(b) on-site steam autoclaving of the waste followed by later shipment toa landfill for burying, and (c) collection of the waste by a licensedwaste hauler with no on-site processing.

Many hospital incinerators, even those located predominately in urbanareas, emit pollutants at a relatively high rate. The EnvironmentalProtection Agency has identified harmful substances in the emissions ofsuch hospital incinerators. They include metals such as arsenic, cadmiumand lead, organic compounds, such as ethylene, dioxins and furans, acidgases and carbon monoxide as well as soot, viruses and pathogens.Emissions from these incinerators may be a more significant publichealth hazard than improper dumping [Steven K Hall, "Infectious WasteManagement: A Multifaceted Problem, " Pollution Engineering, 74-78(August 1989)].

Although steam autoclaving may be used to sterilize waste before furtherprocessing, it is expensive and time consuming. Heat denatures theproteins and microorganisms causing protein inactivation and cell deathin a short time. Temperature monitoring devices such as thermocouples,and biological indicators, such as heat resistant Bacillusstearothermophilus spores, may be used to assure effectivesterilization.

U.S. Pat. No. 2,731,208 to Dodd teaches a steam sterilizing apparatusfor disposing of contaminated waste which incorporates shredding thewaste ("including paper containers such as used sputum cups," col. 1,lines 28-29). Dodd teaches blowing steam into a container full of wasteand processing only limited types of items. The Dodd system has thedisadvantage of depositing the shredded final mixture into a sewer,which would cause further environmental problems.

Whether or not the hospital first autoclaves its medical wastes,including broken needles and glass, the waste is then turned over to alicensed waste hauler for transport to a landfill or other depository.U.S. Pat. No. 3,958,936 to Knight discloses compaction of hospital wastefor more efficient landfill disposal. Specifically, the referenceteaches the application of heat in the range of about 204° C. to 316° C.to hospital and other waste to melt the plastic and convert it into ahard compact block for safer disposal in landfills. The waste isdisinfected by the high temperatures, and sharps, such as needles,become embedded in the plastic where they are a reduced mechanicalhazard. However, this method suffers from the disadvantage of requiringrelatively high temperatures necessitating large energy expenditures andlandfill disposal. Metropolitan landfills are becoming filled, andunauthorized dumping is a problem.

A further area of concern is the sterilization of medical products priorto use. By medical product is meant any product which must be sterilizedprior to use in health care. This is exemplified but not limited toneedles, syringes, sutures, bandages, scalpels, gloves, drapes, andother disposal items. Many reusable items also must be provided insterile form. Widespread current sterilization methods include the useof autoclaving, ethylene oxide, and ionizing radiation such as gammaradiation. The heat and humidity of autoclaving are quite damaging tomany disposable metal products. Ethylene oxide and ionizing radiationare preferred commercially in those cases.

In order to sterilize medical products, poisonous ethylene oxide gas maybe used in a closed chamber containing the products to be sterilized.For effective sterilization, not only must the ethylene oxideconcentration be controlled carefully, but the temperature, humidity,and porosity of the sterilizer load also must be carefully regulated.Ethylene oxide is relatively slow to dissipate from plastics and its usemay require that medical products be stored until the ethylene oxideconcentration decreases to a safe level. Ethylene oxide also must becarefully vented to the atmosphere subsequent to the sterilization cyclein order to avoid poisoning operators of the sterilization apparatus.

Ionizing radiation, such as gamma radiation, may be used to sterilizemedical products within their packaging; however, it must beadministered at such high doses that many plastics become yellow andbrittle due to the gamma rays having altered the structure of thepolymers of which they are made. For example, U.S. Pat. No. 3,940,325 toHirao teaches methods for adjusting the formulas of plastics for medicalsyringes to avoid yellowing and cracking due to exposure to sterilizinggamma radiation. Other substances may also be damaged by exposure togamma radiation. Such ionizing radiation sterilizes because its highenergy photons damage and thereby inactivate the DNA of organisms suchas bacteria and viruses. As a result of the inactivation of the DNA,cells lose their ability to reproduce and thereby cause infections. On alarge scale industrial basis, ionizing radiation, especially gammaradiation from cobalt 60, has been used to sterilize medical productsprior to their use in patients. However, the radiation levels necessaryto sterilize may also damage the product being sterilized.

Other methods have been suggested for sterilization of medical products.For instance, U.S. Pat. No. 3,617,178 to Clouston teaches a method ofimproving sterilization efficiency by increasing hydrostatic pressure.Elevated hydrostatic pressure causes sterilization resistant bacterialspores to germinate, or begin to grow. However, it has no effect onviruses. Bacterial germination, which converts the bacteria from theirenvironmentally resistant spore form, makes the bacteria more sensitiveto radiation, so that lower doses may be employed. Clouston furtherteaches optimizing the hydrostatic pressure effect by adjusting thetemperature up to 80° C. According to Clouston, elevated pressure inheated fluid or moist gas is essential to the method. Elevatedtemperature alone has a negligible effect. Furthermore, the pressure,heat, or moisture treatment taught by Clouston is intended to causebacterial spores to germinate thereby rendering them more vulnerable tosterilization techniques, not to sterilize or inactivate microorganisms.

In contrast, Van Duzer U.S. Pat. Nos. 4,620,908 and Stehlik U.S. Pat.No. 3,704,089 teach prefreezing injectable proteins and surgicaladhesive prior to irradiation with gamma radiation from cobalt 60 foraseptic manufacture of those materials. U.S. Pat. No. 3,602,712 to Manndiscloses an apparatus for gamma irradiation and sterilization of sewageand industrial waste.

Besides gamma radiation, other types of electromagnetic radiation havebeen considered as potential sterilants in known systems. Microwaves areincreasingly being investigated for rapid sterilization of individualmedical devices as well as shredded medical waste. Recently, anexperiment showed that metallic instruments could be sterilized in only30 seconds in a microwave oven (New York Times, "Science Watch MicrowaveSterilizer is Developed," Jun. 20 1989). That particular method,however, suffers from the drawback that only a few such metallicinstruments can be treated at a particular time. It is not particularlyapplicable for treatment of medical waste in bulk, and in particular fortreatment of medical waste which has been bagged.

United Kingdom Patent No. 1 406 789 to Boucher discloses a microwavesystem for the surface sterilization of reusable laboratory, medical,and dental instruments in a moist atmosphere at a lower temperature thanthose presently used and in a shorter time. The system is intended torender aseptic reusable instruments for medical use and generateselectromagnetic energy having frequencies between 100 megahertz and23000 megahertz. Boucher emphasizes that "his invention dealsexclusively with surface sterilization" and that he "does not intend tocover such special cases" as "`in-depth` sterilization" (page 1, lines58-67). Boucher teaches that only through a combination of properhumidification with the thermal and nonthermal effects of microwaveradiation can reproducible and satisfactory results be obtained with awide variety of species, including thermoresistant spores" (page 1,lines 77-83). Boucher teaches the placement of the object to besterilized in a gas-tight container with a source of water vapor.

Soviet Union Patent No. 1,123,705 also discloses a method of sterilizingmedical instruments for reuse by UHF treatment. For injection needles itdiscloses a final temperature of 160° C. to 470° C. and for acupunctureneedles it discloses a final temperature of 160° C. to 270° C.

Systems are also known for treatment of disposable medical wasteutilizing microwaves. This system first shreds the waste, sprays theshredded waste with water, and passes the wet shredded waste through amicrowave chamber designed to raise the temperature of the wet shreddedwaste to 205° C. to sterilize it. After the sterilization step, thesystem compresses the sterilized shredded waste and packages it forshipment to landfills or incinerators (The Wall Street Journal, p. B-3,Apr. 10, 1989). One potential problem with this system is that shreddingbefore sterilization could release infectious particles to theenvironment and may thus spread contagion. Another problem is theultimate disposal of the waste; it persists in landfills or may pollutethe air when incinerated.

Also of interest is a method and apparatus for using microwave frequencyelectromagnetic fields to heat medical waste to disinfect it. "MedicalWaste Treatment By Microwave Technology", Norcal Solid Waste Systems.The system includes equipment for receiving the medical waste, shreddingit into particle sizes of 1 to 1 1/2 inch linear dimension, and applyingsteam to the shredded waste to increase its moisture content, as well asto inactivate certain of the microorganisms thereon. The waste is thencarried to a microwave treatment area where microwave energy heats thewaste to 203° C. for a selected amount of time. A holding area mayprovide heat sealing. The waste is then recirculated to the steamingstation where steam is again applied to inactivate furthermicroorganisms which may still be active in the waste which is shreddedand disinfected, disposed in a dumpster for placement in a landfill. Itmay be appreciated, however, that volumetric heating cannot take placein such a microwave system that the waste has to be scattered in arelatively thin layer on a conveyor belt for treatment by the microwaveradiation as the microwave radiation does not adequately penetrate thematerial. In addition, the material is not enclosed so that there is nosubstantial transfer of moisture from wet materials to dry materials toaid in the heating within the enclosed system.

U.S. Pat. No. 3,547,577 to Lovercheck discloses a machine for treatinggarbage by shredding, compressing the shredded garbage into briquettes,and sterilizing the briquettes with gas. After shredding the garbage isseparated into magnetic and nonmagnetic portions. The sterilization stepemploys ethylene oxide gas which requires temperature control. Thebriquettes are maintained at a temperature of about 54° C.

Further, microwaves are limited in their penetration and are ineffectivefor heating when applied to large scale, boxed medical waste of the typewhich comprises the waste disposal problem today. Microwaves do not heatvery effectively because they do not penetrate very deeply. Most of theheat is generated near the surface and quickly dissipates into thesurroundings, in part because it is not well conducted into the centerportions of the boxed medical waste. In contrast, radio-frequency wavesat relatively low frequency can penetrate boxed medical waste moredeeply.

It also is known in the art that thermal radiation treatment ofbacterial spores and other pathogens may allow greatly reduced ionizingradiation dosage to accomplish sterilization of a given population. Forinstance, in "Thermoradiation Inactivation Of Naturally OccurringBacterial Spores In Soil, . . . " M. C. Reynolds et al , AppliedMicrobiology, Vol 28, No. 3, September 1974, it is disclosed thatbacterial spores may be inactivated by heating them with dry heat andexposing them to ionizing radiation from a cobalt 60 source allowgreatly reduced treatment times over the use of either dry heat orradiation alone.

An attempt to elucidate a model for such behavior is set forth in J. P.Brannen, "A Kinetic Model For The Biological Effects Of IonizingRadiation", Sandia Laboratories, SAND74-0289 (October 1974).

Heat and radiation inactivation of bacteria are discussed at "ProgressReport Beneficial Uses Program, Period Ending Dec. 31, 1976", WasteManagement and Environmental Programs Department, Sandia Laboratories,SAND77-0426 (1977), where it is taught that viruses in sewage sludge maybe destroyed by evaporation. Heat inactivation may be used to destroySalmonella enterititis ser. montevideo. Streptococcus bacteria may bedestroyed by using ionizing radiation at a dose of about 140 kilorads.

The use of cesium 137 to inactivate pathogens in sludge is discussed in"Sludge Or Radiation Disinfection For Beneficial Use", Applied BiologyAnd Isotope Utilization Division 4535, "General Description of theSludge and Radiation Process" SAND80-2744 (December 1980), where it isdisclosed that cesium-137, emitting gamma radiation may be used toinactivate pathogens in sewage sludge. See also, "Use Of Cesium-137 toProcess Sludge for Further Reduction of Pathogens, Sludge or RadiationDisinfection for Beneficial Use," Disease Control Requirements forVarious Sludge Uses, Applied Biology and Isotope Utilization Division4535, SAND80-2744 (Dec. 1980), which discloses that in order to rendersewage sludge safe, in particular for certain agricultural usages,irradiation may be used as an add-on process in conjunction withsterilization where sludge is maintained at 30 min. at a temperature ofat least 70° C. In each of the aforementioned papers, it may beappreciated that the sludge which is being treated is substantiallyhomogeneous in its dielectric characteristics and, thus, in its heatingcharacteristics.

The gamma irradiation equipment commonly used and disclosed in thisapplication is of the type disclosed in "Gamma Processing Equipment",AECL Industrial and Radiation Division (January 1987).

The dual plate about 12 megahertz plate type radio-frequency heater isof the type disclosed in "Dielectric Heating" PSC Inc which althoughundated, constitutes prior art to this application.

Like microwaves, radio-frequency waves are a form of electromagneticenergy. They also transfer energy directly into materials, primarily bythe interaction of their time-varying electric fields with molecules.Radio-frequency waves may be applied by connecting a radio-frequencyalternating current to a pair of electrodes. Between the two electrodesan alternating radio-frequency electromagnetic field having atime-varying electric field component is established. When objects areplaced between the electrodes in the time-varying electric field, thetime-varying electric field partially or completely penetrates theobject and heats it.

Heat is produced when the time-varying electric field accelerates ionsand electrons which collide with molecules. Heat also is producedbecause the time-varying electric field causes molecules, andparticularly those with a relatively high electric dipole moment, torotate back and forth as a result of the torque placed upon them by thetime-varying electric field. Most large molecules, or molecules withevenly distributed charge, have relatively low or nonexistent dipolemoments and are not very much affected by the radio-frequencytime-varying electric field. Small molecules, in particular with polargroups, have relatively large electric dipole moments and thus haverelatively large torques exerted upon them by the time-varying electricfield. In particular, highly polar molecules, like water, experiencerelatively large torques and as a result are rotated by the time-varyingelectric field, thereby transferring mechanical energy to theirsurroundings as internal energy or heat. Lower frequency time-varyingelectric fields penetrate deeply and heat objects more evenly.Relatively high frequency time-varying electric fields do not penetrateas deeply, but heat more rapidly the portions of objects they interactwith.

It should be noted that a time-varying electric field is alwaysaccompanied by a time-varying magnetic field, except where destructivecancellation occurs with interference patterns. For most materials beingconsidered here, the principal heating mechanism arises from theelectric fields. These fields can cause both ohmic heating via inducedionic currents and dielectric heating via molecular stressing from theinternal electric fields. For very moist materials, the presence of theaccompanying time-varying magnetic field can also induce eddy-currentswhich can also heat the material. Also, some type of combined effect ofmagnetic fields and heat may occur. While the ensuing discussion ispresented in context of an electric field effect, it should beunderstood that the effects of accompanying time-varying magnetic fieldare defined here for simplification as part of the electric fieldphenomena.

Because different materials are composed of different types of moleculeswith differing electric dipoles, they heat at different rates whenexposed to a given time-varying electric field. For example, plastics,which are formed of very large polymer molecules, are not heated bytime-varying electric fields as rapidly as water. Metal objects may ormay not be easily heated when exposed to time varying electric fieldseither in the radio-frequency or microwave region. The high conductivityof the metal objects tends to short out the electric fields andrescatter them. As a consequence, there are many conditions where metalobjects are difficult to heat, as exemplified by the metal liner of theinterior microwave ovens. On the other hand, such time-varying fieldscan also induce substantial currents which flow on the outside of themetal objects. Under certain circumstances heating effects will occur onthe surface of the metal object which, in the case of a small needle,the heat is readily diffused into the interior. In addition, thepresence of long, thin metal objects in an electric field causesenhancement of the electric field intensity near the ends of the metalobjects and a diminution or shadowing of the fields near the middle.Thus, if the electric field is parallel to the axis of the metal object,strong electric fields will exist near the tips and weak electric fieldswill exist near the center of the rod or needle. Such field enhancementscan lead to arcing and possible fires. In addition, the fieldsuppression or shadowing of such metal objects is also an unwantedfeature if the presence of a single electric field vector is relied uponin its entirety to provide the sterilization. The failure of theradio-frequency electromagnetic field to penetrate the object causingsurface heating only, or the opposite failure of the materials to absorbthe electric field energy, causes uneven heating of the medical waste.The uneven heating is exacerbated because the medical waste usuallycomprises mixed materials which are difficult to heat effectively usingradio-frequency energy due to the presence of areas of high fieldabsorption, such as are due to metals and concomitant shadowing and coldspots. In addition, similar but less pronounced absorption effects arefound with water molecules. Thus, when heterogeneous or mixed medicalwastes have wet and dry portions, it may be seen that only the wetportions of such material would be heated. Mixed loads such as hospitalwastes were considered impossible to disinfect by radio-frequency energybecause the waste contains a wide variety of materials, each havingdifferent dielectric properties. A great concern was that the presenceof a sufficient number of metallic sharps would lead to arcing, causingignition of the accompanying dry wastes. Another concern was that evenif fire was not started, the differential energy absorption of fluidsand sharps would leave dry objects undisinfected.

In fact, other attempts to kill microorganisms with radio-frequencyenergy have been considered unsuccessful. In his 1980 review, "EffectsOf Microwave Irradiation On Microorganisms", Advances in AppliedMicrobiology 26:129-45, Chipley cites an experiment of applyingradio-frequency energy to bacteria and viruses which grow on tobacco.The experiment found no effect of the radio-frequency energy on thebacteria and viruses. In another study of radio-frequency energy oncontaminated liquid food, there was no showing of "selective killingeffect" except when ethanol was added.

In the same review, Chipley cited numerous tests of microwaves onmicroorganisms and concluded that "results of tests for viability of B.subtilis spores also showed identical death curves compared with thoseobtained by conventional heat." On the other hand, however, Chipleycites several references which support the view that microwaveirradiation has collateral thermal and nonthermal effects. [For example,Culkin and Fung (1975) found that microbial destruction occurred atreduced temperatures and shorter time periods when the material wasexposed to microwaves as compared to conventional heating methods.Wayland et al., 1977 also demonstrated the interdependence of heat andmicrowaves effects in the studies of spores of B. subtilis.

U.S. Pat. No. 2,114,345 to Hayford discloses a radio-frequencyapplicator with electroscopic control for destroying bacteria in bottledbeer and similar products. Hayford teaches an apparatus for sterilizinga series of small objects. The radio-frequency field must be constantlyreadjusted by the electroscopic control. There is no teaching orsuggestion that large scale sterilization of heterogeneous waste couldbe carried out.

U.S. Pat. No. 3,948,601 to Fraser et al. teaches the indirect use ofradio-frequency energy in sterilizing medical and hospital equipment aswell as human waste. The reference teaches the use of radio-frequencyenergy for heating gases, particularly argon, and exciting them so thatthey ionize into a plasma having a temperature of approximately 100° C.to 500° C. The reference teaches that a cool plasma at a temperature ofonly 25° C. to 50° C. and very low pressure may effectively sterilize anarticle. However, sterilization by plasma does not suggest the directuse of radio-frequency waves in sterilization since it is the chemicalreactive effect of the plasma which presumably performs thesterilization function rather than the direct or thermal effects ofradio-frequency energy on pathogens contained on the material. It may beappreciated that only those portions of the equipment and waste actuallycontacted by the plasma would be treated.

Reprocessing of the waste, and especially medical waste, is also vitalfor several reasons. Even if the medical waste has been renderedharmless or innocuous by the destruction of any pathogens associatedtherewith, there is still the problem of the disposal of the bulkmaterial including the plastics, the sharps, and fibrous material suchas gowns, diapers, and the like. The material is relatively bulky andlandfills, particularly in many urban areas, have become filled. Inaddition, older landfills may leak and nonpathogenic but chemicallypolluting substances may leak into surrounding ground water, causinghealth hazards. Thus, burying the sterilized medical waste is becomingless attractive. Further, merely burning the sterilized medical wastecan pollute the atmosphere and cause acid rain. Current reprocessingtechnology should be employed to process the disinfected medical wastefor effective utilization and proper disposal. What is needed is amethod for disinfecting the medical waste and destroying the pathogensthereon and disposing of the disinfected waste in a manner which isharmless to health care workers, waste handlers, and the public atlarge.

A series of investigations has been undertaken as to sterilization,especially for food. This has resulted in patents or inventions whereinthe material to be treated is housed in a microwave transparentcontainer such that the material can be heated at vapor pressures whichcoexist with temperatures of 120° C. These include Gray U.S. Pat. No.3,494,723; Nakagawa U.S. Pat. No. 4,808,782; Stenstron U.S. Pat. No.4,808,783; Landy U.S. Pat. No. 3,215,539; Utosomi U.S. Pat. No.3,885,915; and Fritz U.S. Pat. No. 4,775,770. All of these patentsdisclose heating homogeneous material in some form of pouch or pressurecontainer where the material, typically food, is homogeneous. They donot address the special problem considered here where the material isheterogeneous and contains sharps, moist materials and dry materials.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for processingmedical materials such as medical and veterinary waste and medicalproducts which disinfects the materials by heating them withradio-frequency energy. The invention disinfects bulk medical waste byheating it with a radio-frequency electric field. The medical waste isheterogeneous, that is, it comprises wet and dry materials such asdressings, diapers, tissue and the like and material such as plasticgloves, plastic syringes and the like. The medical waste also containsmetal containing sharps as such hypodermic needles, suturing needles,scalpels and the like. The waste is exposed to a radio-frequencyelectric field having a frequency of in the range of 500 kilohertz to600 megahertz, preferably about 10 megahertz to about 100 megahertz. Thelower frequencies of operation are preferred to assure good depth ofpenetration of the electric fields into the more moist material. Ifmicrowave frequencies are used (above 900 MHz), the depth of penetrationis often less than a few centimeters. The depth of penetration isdecreased by increasing the moisture content.

While not wishing to be bound by any particular theory, it is noted thatthe time-varying electric field heats the water on the wet portions andboils off a portion of it. The evaporated water or water vaporapparently travels by convection and diffusion throughout the bagcontaining the medical waste and may condense on the cooler, dryportions because, other than the metal-containing sharps, dry materialhas not been heated substantially by the time-varying electric field. Itis believed that the condensation of moisture on the formerly drymaterial gives up heat of vaporization and thereby transfers heat to thepreviously dry material. It is believed that this transfer of moisturemakes the materials relatively homogeneous with respect to watercontent. This permits all of the material to be rapidly heatedvolumetrically by the field. The condensed moisture on or in thepreviously dry material can now absorb energy from the electric field.This generates heat within or on the previously dry material which isnow rapidly heated by the field. In one embodiment of the invention, thebags of medical waste are confined within pressure vessels within theelectric field and the medical waste is rapidly heated above 90° C.Nevertheless, this temperature kills the pathogens on the waste.

One step of the pressure-vessel method comprises heating the medicalmaterials with radio-frequency energy, possibly within one or more bagshoused within a closed container, to raise the internal temperature toabout 90° C. In another embodiment, the temperature may be raised to100° C. The pressure within the bags, if used, increases to a pointwhere the bags will burst thereby interconnecting the fluids among thebags within the container to permit vapor transfer from one bag toanother. The heating may then continue to 120° C.

The vapor-containing version of this invention is suitable to treat awide variety of wet and dry conglomerations of permeable material whichmust be raised to temperatures below or close to that of thevaporization point of water. The use of radio-frequency heating in sucha container creates volumetric heating and reduces the time requirementsassociated with autoclaving. The invention also is useful for thetreatment of certain nonuniform moisture content commodities which arehighly permeable, such as breakfast cereals, tobacco, and whole grains,which are highly permeable to gas flow and at the same time oftenrequire heating treatments to disinfect the produce, to kill insectinfestations and to equalize the moisture contents.

In another embodiment, to implement the vapor-containing version of theprocess, the materials to be treated may be collected and eventuallyplaced in a plastic bag capable of withstanding temperatures, for about15 minutes, of just above the vaporization point of water which, in thiscase for sea-level atmospheric pressure, would be just above 100° C.When the bags are filled, these are sealed and placed in a fiberboardbox container. An additional vapor seal such as a fiber reinforcedplastic sheet, plastic sheet or cylinder may be applied over a number ofboxes which can then be placed in a container for ease of transportthrough the RF heating facility. The additional vapor seal confines thematerial up fifteen psig or more.

Thus, by selecting this type of specific packaging, several of therequirements for the successful vapor-containment, disinfection processare realized. First of all, a vapor impermeable barrier is placed aroundthe material. Secondly, the heat capacity of the vapor barrier is smallsince the wall thickness of the plastic material is quite thin. Thirdly,thermal transfer outside the treatment material is inhibited by the useof the fiberboard box. Such fiberboard boxes are relatively good thermalinsulators, owing to the air-sack-like spacing between the inner andouter portions of the fiberbox material. Finally, the outer plastic orfiberglass reinforced vapor prevents intimate contact between thecombustible fiberboard or portions of the medical waste with outsideair.

One of the embodiments of the invention additionally comprises the stepof transferring heated medical waste to a heat-soaking area whichmaintains the elevated temperature for about 45 minutes. The temperatureis maintained in an energy effective and cost efficient fashion in orderto provide extra assurance that all pathogens are destroyed by the heat.processed.

However, it may be advantageous in certain situations not to treat thematerial or waste in a pressure resistant container, but rather thematerial can be exposed in an unpressurized container to theradio-frequency energy such that the temperature of the material ormedical waste is first heated to about 90° C. Further heating to atleast 120° C. substantially evaporates all of the water contained in themedical waste. Hence in another embodiment of this invention, to avoidpossible underheating effects associated with shadowing through thepresence of metallic objects in the waste, the material in the containercan be tumbled such that all portions of the material are exposed to allthree vector orientations of the electric field.

The tumbling process also ensures exposure of all the material to theelectric fields to take advantage of collateral thermal and nonthermaleffects which may exist at about 90° C. and may allow completesterilization to be accomplished without a significant degree ofvaporization.

Another embodiment of the invention also comprises steps of furtherprocessing the medical waste by presorting the material into recyclableplastic or refuse derived fuel, comminuting or shredding both types ofmaterials, repackaging and shipping to commercial users.

In a still further embodiment of the invention, the medical material,specifically comprising medical and veterinary waste, is received forprocessing. The waste is then comminuted or shredded to an averagelinear particle dimension of 1 to 2 inches. If the waste is particularlydry when it is packed in a container for processing, water or foam maybe added to the waste. The foam specifically comprises a surfactant suchas a detergent mixed with water. The shredding reduces the particle sizeand reduces the field intensities in any metal materials in theparticles in order to reduce the likelihood or intensity of arcing whenthe shredded material is exposed to the radio-frequency radiation. Thecontainer also may be lined with wet material, such as wetted cardboard,to increase its RF absorption.

In most cases, water need not be added to the material as the materialcontains up to ten percent water by weight. Thus, when the material isheated by the radio-frequency field, water from the wet material isvaporized, transported to the dry material where it condenses, andcouples with the radio-frequency radiation to heat the dry material. Inthe event that water is to be added, it may be added to the container inseveral ways. First, it may be sprayed on in the form of a mistingstream or may be simply be used to soak the shredded material. If largeamounts of water, however, are used, the radio-frequency energy may besubstantially reflected away from the interior of the container causingthe processing time to increase or requiring that higher power equipmentbe used to obtain reasonable heating times. In order to reduce theamount of reflection, the water may be added in the form of foam whichis volume filling, but which has a relatively low average dielectricconstant. In experiments which we have performed, foam having adielectric constant of about 1 to about 10, rather than 80, has beenemployed, causing only about 10% of the input power at about 10megahertz to be reflected, rather than about 90% of the input power, ashappens with volumes of liquid water. The foam also provides a quenchingmedium for reducing the likelihood of fires within the container.

One advantage of the above-mentioned pressure vessel which retainsvapors up to temperatures of at least 120° C. is obtaining sufficientutilization of the radio-frequency energy by not allowing the watervapor to escape. Thus, energy losses which might occur in anonpressurized container due to the need to vaporize the water areavoided.

In some versions, the walls of the cavity or belt are heated to atemperature that is comparable to the temperature of the material beingprocessed. As a consequence, in the case of the invention at hand,little or no energy is transferred out of the items to be heated. Thepurpose of minimizing this transfer is that if the surface is too hot,the material becomes sticky and gummy and thereby eventually clogs themechanics of the system. On the other hand, if the wall material issignificantly lower than that of the material being processed, energy islost from the material being processed. In the case of wet or moistmaterial where a high energy absorption occurs, this may not be asignificant problem, but it can be significant in the case of very drymaterials. These have little dielectric absorbing ability and thereforehave little capability to simultaneously heat themselves and theadjacent walls. To overcome this, a preferred embodiment of theinvention employs the use of peripheral guard heaters along the wallssuch that the wall temperature assumes approximately the sametemperature as that of the material being processed. Alternatively,insulated wall materials may be used which have low thermal conductivityand heat capacity, whereby the heated gases from the material beingprocessed can easily heat the wall so that they can be heated such thatthe wall temperature can immediately rise to the temperature of thematerial being

The container may be comprised of epoxy fiberglass and is sealed, andmay either have a pressurated seal or nonpressurated seal. With thenonpressurated seal, the container will vent moisture at 100° C. With apressurated seal, the container may be pressurized to about 15 lbs. persquare inch above ambient or more, allowing the medical material thereinto be heated to 120° C. or more, causing complete disinfection of thematerial within rapid time.

Before the medical materials are heated, they may also be compacted toallow more material to be heated at any one time and to cause thedielectric material, including the foam and insulating material in themedical waste, to be driven into more intimate contact with any metaltherein, causing a reduction in the likelihood of arcing and fires inthe medical material when it is heated. Reduction in fires is alsoachieved in this alternative method by the use of the sealed containerscomposed of the fire-resistant plastic, which limits the amount ofoxygen within the container, to prevent fires from spreading if arcingcauses partial combustion of the contents.

In a still further alternative embodiment, the radio-frequency treatmentchamber may be a pressurized radio-frequency treatment chamber which canreceive relatively low strength plastic containers whose interiorpressure may be equilibrated to the pressure within the pressurizedradio-frequency chamber. The medical materials then have theradio-frequency energy applied to them to heat them to approximately120° C. so that the materials are rapidly disinfected by heating due tothe applied radio-frequency energy, and possibly also due to the directelectric field effects of the radio-frequency energy on themicroorganisms, including viruses, bacteria, and bacterial sporestherein.

Therefore, in view of the foregoing, it is a primary object of thepresent invention to render harmless or disinfect medical materials byheating them with radio-frequency waves. A further object or aspect ofthe invention is to dispose of disinfected medical and veterinary wastein an environmentally safe manner. Additional objects, advantages, andnovel features of the invention will be set forth in part in thedescription which follows, and in part will become apparent to thoseskilled in the art upon examination of the following, or may be learnedby practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of the steps involved in rendering baggedmedical waste innocuous by heat treatment with radio-frequencyelectromagnetic fields;

FIGS. 2A, 2B, 2C and 2D are schematic representations of radio-frequencytreatment units and radio-frequency energy sources which may be used inthe radio-frequency disinfection of infectious medical waste;

FIG. 3 is a schematic view of a system for continuously disinfectingbagged and boxed medical waste by using radio-frequency energy;

FIG. 4 is a section of a radio-frequency reactor of FIG. 3, showing theelectric field vector lines and equipotential lines generated within theradio-frequency treatment unit;

FIG. 5 is an isometric view of the radio-frequency treatment unit ofFIG. 3 and a conveyor associated therewith showing details of theorientation of the conveyor with respect to an exciter plate within thereactor and the radio-frequency treatment unit;

FIGS. 6A, 6B and 6C are plan and front side elevational views of adifferent type of radio-frequency treatment unit which can be usedwithout the exciter plate, the top and bottom of the shielded cavityserving as termination points for the electric fields, therebysimplifying the cavity design and permitting operation at higherfrequencies.

FIGS. 7A, 7B and 7C are graphs of a normalized frequency power densityin a single-end driven radio-frequency treatment unit and aradio-frequency treatment unit driven at opposite ends byradio-frequency energy having two different frequencies to provideuniform average power throughout a major portion of the treating chamberof the unit;

FIG. 8 is a schematic view of a semicontinuous waste disinfect systememploying the radio-frequency treatment unit illustrated in FIGS. 6A, 6Band 6C;

FIG. 9 is a flow diagram showing the steps of waste disinfection carriedout by the apparatus of the present invention;

FIG. 10 is an elevational view, shown partly in section, of a pressurevessel for holding bagged medical waste for placement inside theradio-frequency reactor of the apparatus of the present invention;

FIGS. 11A and 11B show side and end elevational views of the pressurevessel of FIG. 10 and the mounting and driving apparatus therefor;

FIG. 12 is a diagrammatic view of the vapor treatment system associatedwith the apparatus shown in FIGS. 3 and 8; and

FIG. 13 is a diagrammatic representation of an alternative vaportreatment system employing condensation and waste treatment;

FIG. 14 is sectional view of another container for receiving medicalmaterial to be disinfected;

FIG. 15 is a block diagram of another radio-frequency treatment systemembodying for disinfecting medical materials; and

FIG. 16 is a flow diagram of the steps of treating medical materials ofthe system shown in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of the instant invention is illustrated in the flow diagramof FIG. 1 and consists of gathering medical waste from a waste source ina step 2 and placing the waste in a thermally insulated vapor sealedcontainer, which may consist of a plastic bag, in a step 3. In a step 4,the vapor sealed container may be placed inside a box and the box loadedon a pallet. The box and pallet are then sealed in a vapor sealcomprising a shrink-fit plastic or the like to prevent the escape ofmoisture from the container during processing. The vapor sealedcontainers are placed in a radio-frequency field applicator in a step 5and a radio-frequency power source energizes the applicator to heat thematerial for a sufficient time to evaporate some of the water therein,transfer the resulting water vapor to dry portions of the material whereit condenses and wets providing additional absorption and thereby heatsthe entire volume of medical waste in a step 6. After heating of themedical waste is completed and the waste is disinfected by heatinactivation of the microorganisms thereon the disinfected medical wastemay be converted to a refuse-derived fuel or may be transferred to alandfill in a step 7.

Referring now to the drawings and especially to FIG. 3, an apparatus 10for continuous waste treatment is generally shown in FIG. 3 and includesa radio-frequency treatment unit 12 and a waste transport system orconveyor 14 for feeding bagged and/or boxed heterogeneous medical waste16 to the radio-frequency treatment unit 12. A source of radio-frequencyenergy 18 is connected to the radio-frequency treatment unit 12 toenergize it and an effluent handling system 22 is connected to theradio-frequency treatment unit 12 to treat gases and vapors evolvedduring the heating of the bagged and boxed medical waste 16. Also asource 20 of inert sweep gas, such as nitrogen, is connected to theradio-frequency treatment unit 12 for driving oxygen therefrom to avoidcombustion of the medical waste being heated.

The radio-frequency treatment unit 12 includes an applicator or reactor34 providing a reaction chamber to which radio-frequency energy isapplied. The design of the applicator 34 to produce the requiredelectric field and exposure time is of interest. Such applicators may bedivided into three basic groups: (1) TEM parallel plate applicatorswhere the wavelength of the excitation frequency is large or comparableto the dimensions of the reactor 34; (2) TE or TM controlled modeapplicators where the dimensions of the reactor 34 are comparable to orseveral times the wavelength of the excitation frequency; and multi-modeTE and TM applicators where the maximum dimension of the reactor 34 istypically 4 or more times the wavelength of the excitation frequency.Typically with the multi-mode TE or TM applicators, the modes are notcontrolled such that a number of peaks and nulls of the electric fieldexist within the heating unit, such as exists typically in a microwaveoven.

FIGS. 2A, 2B, 2C and 2D illustrate the transition from a parallel plateTEM applicator 34 to a controlled limited mode TE or TM applicator. FIG.2A shows a reactor 34 formed of two parallel plates 66 and 70 with thematerial 16 placed between the upper and lower plates 66 and 70,respectively. Voltage is applied between the upper and lower plate bymeans of a tuning coil which is driven from the RF source 18. As long asthe wavelength of the applied voltage is large compared to thedimensions of the applicator 34, and the box 16 is well within theextended portions of the metal plates 66, 70, a uniform field can beapplied.

The applicator shown in FIG. 2A is an example of the TEM applicator andis limited to the lower frequencies, and because the dielectricabsorption is roughly proportional to the "nth" power of the frequency(where n ranges from 0.3 to 1.0 for frequencies below about 300 MHz) andthe square of the electric field strength, substantially higher electricstrengths for lower frequencies are required to cause the same heatingeffect as might be expected for higher frequency operation. Higherfrequency operation is possible in a controlled mode heating cavity 34such as shown in FIG. 2D, which is an example of the controlled mode TEor TM applicator. The transition of the reactor 34 from the embodimentof FIG. 2A to that shown in FIG. 2D is illustrated in FIGS. 2B and 2C.The parallel plates 66, 70 shown in FIG. 2A are resonated with the thinwire series inductance 67. However, by reducing the value of thisinductance, higher frequency resonances are possible. Nevertheless,there is an upper limit to the frequency at which this resonance can bemade to occur if just a single thin wire solenoidal inductor isemployed. To increase the resonant frequency, straps 69 on the sides ofthe two parallel plates 66, 70 can be employed as shown in FIGS. 2B and2C, with power applied by way of a launching coil or turn 67. Eventuallythis arrangement is transformed into the controlled mode TE or TMapplicator as shown in FIG. 2D. The controlled mode TE or TM applicator34 is defined where 1/2 wavelength is comparable to one of the largerdimensions of the box. This limits the number of permissible modes andallows controlled and uniform heating. In the case of a microwave oven,the dimensions are in the order of 6 to 8 half wavelengths. This resultsin uncontrolled modes and nonuniform heating.

In another embodiment, as may best be seen in FIG. 3, the wastetransport system 14 also includes a conveyor motor 24 which drives aninput conveyor drum 26.

An output idler conveyor drum 28 also comprises a portion of theconveyor 14 and a conveyor belt 30 engages both the input driven drum 26and the output idler drum 28. A portion 32 of the conveyor belt 30extends through the radio-frequency treatment unit 12 for carrying thecontainerized medical waste 16 therethrough for treatment.

The radio-frequency treatment unit 12 comprises a radio-frequencychamber 34 having a radio-frequency chamber inlet opening 36 and aradio-frequency chamber outlet opening 38. The radio-frequency treatmentunit 12 has a length of 18 meters, a width of 4.5 meters and a height of3 meters. The radio-frequency chamber 34 comprises a bottom wall 40, atop wall 42, an inlet wall 44, an outlet wall 46, a first side wall 48,and a second side wall 50. Each of the chamber walls is constructed ofhighly conducting material such as copper or aluminum. Typically 6millimeter aluminum can be used, which allows the chamber walls to beself-supporting. Also 3 millimeter thick copper could be used inconjunction with additional physical support. The radio-frequencytreatment unit 12 also includes an inlet tunnel 52 connected to theinlet wall 44 at the inlet opening 36. The inlet tunnel 52 has arectangular cross section and is dimensioned to act as a wave guidebelow cutoff to prevent the radiation of electromagnetic fields from theinterior of the radio-frequency chamber 34 to the environment whileallowing the containerized medical waste 16 to be carried freely intothe radio-frequency chamber 34 by the conveyor belt 30. Likewise, a waveguide below cutoff forms an output tunnel 54 from the outlet 38 at theoutlet wall 46 to carry containerized disinfected medical waste 16 outof the vicinity of the radio-frequency treating chamber 34 withoutallowing radio-frequency energy from the radio-frequency treatingchamber 34 to leak into the surroundings.

In order to energize a radio-frequency electromagnetic field and, inparticular, the time-varying electric field component thereof, withinthe radio-frequency treating chamber 34, the radio-frequency energygenerator 18 is provided and includes a radio-frequency currentgenerator 56 connected to a coaxial cable 58 for feeding powertherethrough. A matching network 60 receives the radio-frequency energyfrom the coaxial cable 58 to which it is connected. A second coaxialcable 62 is also connected to the matching network 60 to carry theradio-frequency power therefrom. That coaxial cable has a center lead 64which penetrates the top wall 42 of the radio-frequency chamber 34 andis connected to a vertically movable substantially rectangularconductive exciter plate 66. The outer conductor is connected to the topwall 42 and grounded. The exciter plate 66 is suspended by a pluralityof nonconductive ropes 68, preferably nylon or orlon, from the top wall42 of the radio-frequency chamber 34. This allows the exciter electrode66 to be moved with respect to the containerized medical waste 16 toprovide a spatially uniform, time-varying electric field to heat thecontainerized medical waste 16 relatively uniformly. A three millimeterthick copper bottom plate 70, which is substantially flush with a pairof bottom plates 72 and 74 of the inlet and outlet wave guide belowcutoff tunnels 52 and 54, respectively, comprises the bottom plate ofwhat is in essence a biplate configuration reactor. Typically, thebottom plate 70, as well as the walls 42, 44, 46, 48, 40, and 50 of theradio-frequency chamber 34, are maintained at ground potential while theexciter plate 66 is excited by the radio-frequency energy fed throughthe coaxial cable 62.

It is particularly important in the practice of the present inventionthat the exciter plate 66 be movable, as this allows adjustment of therelatively uniform portion of the electric field within theradio-frequency chamber 34. This is important because the size of thecontainers containing the containerized medical waste 16 may vary fromtime to time. It is important that when the containers are travelingthrough the center portion of the radio-frequency heating chamber 34,they be subjected to a substantially spatially uniform time-varyingelectric field so that the contents thereof are uniformly heated.

In the case of the parallel plate exciter, the dimensions of the box 16compared with the dimensions of the electrode 66 are important in orderto assure reasonably uniform electric field and resultant heatingeffects. To determine the relationship between the box dimensions andthe size of the electrode exciter, the data in FIG. 4 were developed.This shows equi-potential lines (horizontal) coupled with thedisplacement current lines (near-vertical) for a limited extent exciterelectrode 66 centrally located in a large conducting box. The relativeelectric field at any location can be developed by determining thedimensions of a square at any location and a similar square in theuniform region (far right) and dividing the maximum dimensions of thisuniform field square by a similar dimension of the square at the desiredlocation.

It can be seen therefore, if the guard distance, that is the distancefrom the edge of the box to the downward projection of the edge of theelectrode, is equal to the height of the electrode, that very littlefield distortion occurs and that the electric field in the region to theright of this point is reasonably uniform. Further studies show that ifthe edge of the box is moved farther to the left, field distortionoccurs such that the electric field is significantly less near theground plane and therefore the material of the box would experience asignificantly lower heating rate. Guard distances which are equal toabout one-fourth or less than the height of the exciter electrode arerelatively unsatisfactory.

On the other hand, it is seen that as the height of the box isincreased, the field distortion near the edge of the electrode is suchas to contribute excess field intensities, particularly where the heightof the box is 75% of that of the exciter electrode and the guarddistance is equal to one-quarter of the electrode height. Data takenfrom this plot are summarized in Table 1. It may be seen that guarddistances as little as one-fourth the height of the electrode areacceptable but, on the other hand, the maximum height of the boxprobably should preferably be no more than 67% of the height of theexciter electrode. The reason for this is that as the box enters fromthe left going into the right, it encounters increasingly high levels ofelectric field near the edge of the electrode. As a consequence, excessfield intensity can occur there which can lead to potential gradientsand arcing phenomena. To ensure against such effects as well as over orunder heating, the normalized heating rate during entry wear the topedge of the box should not vary more than 1.5 to 1.0 for the parallelplate type of heater shown in FIG. 3. Where the bulk of the water is notevaporated but rather repositioned, heating ratios of 2.0 to 1.0 can betolerated. Where the bulk of the water is evaporated and heating iscontained beyond the vaporization point, the heating rate variationshould be less than 1.5 to 1.0.

                  TABLE 1                                                         ______________________________________                                        HEATING POTENTIAL (E.sup.2) NORMALIZED TO                                     THE HEATING POTENTIAL IN THE UNIFORM FIELD                                    REGION AS A FUNCTION OF THE BOX HEIGHT                                        RELATIVE TO THE HEIGHT OF THE ELECTRODE                                       AND FOR RELATIVE GUARD LENGTHS.                                               Dimensions Relative                                                                             Normalized Heating                                          to Electrode Height, h                                                                          Potential, (E.sup.2)                                        Box      Guard   Top of   Bottom of                                                                              Top of Box                                 Height   Length  Box      Box      During Entry                               ______________________________________                                        0.5      0.5     0.92     0.96     1.0                                        0.5      0.25    0.92     0.88     1.0                                        0.67     0.5     1.25     0.96     1.21                                       0.67     0.25    1.10     0.88     1.21                                       0.75     0.5     1.44     0.96     1.8                                        0.75     0.25    1.2      0.88     1.8                                        ______________________________________                                    

In the present embodiment, in particular for the type of reactor shownin FIG. 3, a 12 megahertz radio-frequency current generates a 12megahertz radio-frequency electric field within the radio-frequencychamber 34 to heat the medical waste 16 within the hospital wastecontainers. It may be appreciated that the hospital or medical waste maycomprise a wide variety of waste having many different dielectricconstants. For instance, the sharps will include metals in whichcollected displacement currents will be induced by the time-varyingelectric field. Very moist materials will also be included, as well asquite dry materials such as gloves and the like. In particular, themoist materials couple well with the radio-frequency field due to thefact that the dipole moments of the water molecules cause the watermolecules to have a torque exerted thereon by the electric field when itis unaligned with the dipole moments. This causes the molecules to bemoved, in particular rotated by the field. The water molecules thentransfer disordered kinetic energy to the materials upon which they arein contact, causing them to be heated.

When the medical waste 16 is first placed in the radio-frequency chamber34, the wet portions of the medical waste 16 are rapidly heated by theradio-frequency energy, causing water vapor to be evolved therefrom. Thewater vapor is dispersed by convection and diffusion throughout the bagsof hospital waste and condenses on the dry waste therein, due to thefact that the dry waste has been relatively unheated until it comes incontact with water. The condensation of the water vapor on the coolermaterial transfers heat thereto by giving up heat of vaporization. Moreimportantly, however, the condensed vapor wets the formerly dry materialwhereby the water is volumetrically heated by the time-varying electricfield, thereby generating thermal energy in the previously dry waste andcausing the waste within the container to be substantially uniformlyvolumetrically heated. Since the frequency of the time-varying electricfield is selected to be 12 megahertz, or, in the alternative 64megahertz, the electric field penetrates well into typical waste bags,and the entire volume of medical waste within the bags is substantiallyuniformly heated once the water is dispersed, allowing the waste to berapidly heated. Once a minimum temperature of about 90° C. is reached,virtually all pathogenic organisms are all destroyed by the heat, andthe waste is disinfected.

In one embodiment of the invention, as shown in FIG. 3, the exit tunnel54 is lined with electric resistance heaters 80, which are means forheat soaking the medical waste, if a further margin of safety isdesired. As the containerized medical waste 16 passes through the exittunnel 54, the electrical resistance heaters 80 transfer sufficient heatenergy via radiation to prevent heat loss from the waste 16. This heatis not sufficient to raise the temperature of boxes 16 further, but itis only sufficient to maintain the temperature of the boxes at the exit.As a result, the exit tunnel 54 in combination with a similar tunnel 54aof much longer length will provide a means for heat soaking the medicalwastes over the appropriate period of time. This can be done with arelatively low power consumption in order to hold the medical waste atthe desired temperature for up to approximately 45 minutes. In addition,such a heating tunnel in combination with the RF source heating methodprovides a means to heat the medical waste in a controlled manner suchthat combustion does not occur and the plastic does not melt orpartially pyrolyze. It would, of course, be difficult, if notimpossible, to use such electric resistance heaters or other infraredradiative heaters solely to heat bulky materials like the hospital wastefrom ambient temperature due to the fact that infrared heaters provideessentially surface and not volumetric heating. That is, in accordancewith the present invention, the waste is first heated volumetrically tothe desired temperature and held at that temperature by surface heating.If the surface is maintained at the desired temperature, the interiorcannot cool.

Doors may be provided at the distal ends of the inlet wave guide belowcutoff 52 and the outlet wave guide below cutoff 54 as well as the heatsoak entrance and exit to trap gases generated by the heating within theunit. These gases might, like the contents of the medical wastecontainers 16, be combustible. As a result, the inert gas system 20floods the radio-frequency heating chamber 34 as well as the inlettunnel 52 and the outlet tunnel 54 with nitrogen. The flow is a counterflow in the inlet tunnel 52 keeping oxygen out of the system in order toprevent fires. The nitrogen flush also provides other important featuresto the invention. Since the injection point for the nitrogen flush isnear the inlet tunnel 52, or actually on it, the relatively coolnitrogen enters the radio-frequency treating area at approximately thesame temperature as the waste 16. Nitrogen is carried in the samedirection as the waste 16 and is heated thereby by conduction, radiationand convection from the heated medical waste 16. As a result, aneffective temperature ramp is provided from the inlet portion of theradio-frequency heating chamber 34 to the outlet portion by the flowingof the gas in combination with the gradual heating. Due to the fact thatthe gas flows in the direction in which the temperature is increasing,refluxing of any vapors released from the containerized medical waste 16is prevented to the cooler input hospital waste by the directed flow ofthe nitrogen gas and thus prevents condensation on the cooler exteriorof the containers, which could inhibit volumetric heating. The nitrogengas also operates as a sweep gas and carries effluents out through aneffluent exit port 82 which comprises a portion of the inert gas system20. The effluent exit port 82 is connected to a blower 84 which isconnected to the effluent treatment system 22.

The effluent treatment system 22, as may best be seen in FIG. 12,processes the effluents evolved in the heating of the infectious medicalwaste. These effluents essentially consist of steam, air and inertgases, such as the nitrogen sweep gas, as well as some hydrocarbonsgenerated during heating of the waste and possibly pathogens that mighthave been released during the waste processing. Under normal conditions,though, all of the pathogens would be inactivated or destroyed by theradio-frequency heating. The effluent exits through the duct from theradio-frequency heating chamber 34 and passes a hydrocarbon sensor 92connected to the duct 82 for determining whether hydrocarbons arepresent. If hydrocarbons are present in excess of a predetermined value,an air injection system 94 injects air into the effluent gas stream sothat a combustible mixture of air and hydrocarbons, as well as inertgases, is fed to a vapor preheater 96. The vapor preheater is a heatexchanger fed with exhaust gases from downstream equipment. Ahydrocarbon sensor 98 is connected to a condenser duct 100 adapted toreceive an inlet from the condenser. The gases are then fed through aduct 102 to a catalytic oxidation system 104 which may be purchased fromAllied Signal UOP or other commercial suppliers. The catalytic oxidationsystem receives fuel such as propane or natural gas, if needed, via afuel delivery line 106. The catalytic oxidizer also includes a catalyst,such as Torvex catalyst available from Englehart, for the oxidation ofhydrocarbons into carbon dioxide and water. The oxidizable componentsare oxidized by contact with the catalytic oxidizer and resulting hotcombustion products are fed through a combustion output line 108 to ablower 110 which directs the hot combustion products through a hot gasoutput line 112 into the heat exchanger 96 to conserve heat energy bytransforming heat from the hot combustion products before they arevented to the environment to the effluent gases in the input duct. Thecombustion products are then vented through the output duct 100 to theenvironment. The hydrocarbon sensor 98 will signal an alarm if unburnthydrocarbons are passing through the output duct 100, causing a systemshutdown to allow correction or alteration of the system parameters toensure complete combustion of all combustible effluents. The combustionof the combustible effluents also destroys any pathogens which may betrapped therein and which had remained active before combustion.

In an alternative system, the radio-frequency chamber 34, as may best beseen in FIG. 13, is connected to an effluent output line 111 havingelectrical resistance heating elements 113 wrapped thereabout tomaintain a high temperature of the output effluent, thereby preventingany heavy fractions from condensing within the duct 111 and alsodisinfecting the effluents. Thermal insulation 114 is also wound aboutthe heating elements 113 to prevent excessive heat loss from theelectrical heating elements and also to prevent condensation of heavyfractions within the duct 111. An air cooled vapor cooling system 116,which in the alternative may be water cooled, causes condensation ofheavy fractions into liquid which may then be passed by a duct 18 to ademister 120. The demister 120 separates any remaining gas flowingthrough the duct 118 into a gaseous fraction which is fed on a gas line122, and a liquid fraction fed via a liquid line 124. A carbon adsorbentsystem 126 receives the gas from the line 122 and vents any inert gasesleft over through a line 128 which is connected to a venting blower 130.The venting blower 130 feeds the remaining inert cleaned gases throughan output duct 132 to the environment. Similarly, the liquids are fedvia the duct 124 to a liquid adsorbent system 134 which is filled with acommercially available adsorbent material for water cleaning, such asFiltrasorb from Calgon. As an added precaution, clean water is then fedvia duct 136 to a pump 138 which passes the clean water through a pipe140 to a sterilizer 142 which heats the water to 90° C. forsterilization. The sterilized water is fed via a duct 144 to a receivingcontainer 146 which receives and stores it. The sterilized water maythen be disposed of in an appropriate manner.

As may best be seen in FIG. 8, an alternative semicontinuous wastesystem 200 is shown therein, utilizing the radio-frequency system shownin FIG. 6. The semicontinuous waste disinfection system 200 includes aradio-frequency waste treater 202 and a waste transport system 204. Aradio-frequency energy generator 206 is coupled to the radio-frequencywaste treating reactor 34. In operation, the radio-frequency energygenerator 206, which includes a control system 208 connected via a cable210 to a radio-frequency power source 212, generates radio-frequencyenergy in response to control signals from the control 208 and feeds theradio-frequency energy via a cable 214 to a matching network 216. Thematching network 216 has a power delivery cable 218 connected to itwhich has an inner conductor 220 terminating at a field exciter 222 of aloop type or other suitable type. A dielectric plug 224 terminates anend of an insulating jacket 226 of the coaxial cable and mates with anupper wall 203 of the radio-frequency waste treating reactor 34. Theradio-frequency waste treating reactor 202 also includes a bottom wall232, an inlet wall 234, an outlet wall 236, and a pair side walls, oneof which is shown as a first side wall 238. Coupled to the treatmentchamber is an inlet wave guide below cutoff tunnel 240 which issubstantially rectangular in cross section, connected at an inlet 242 tothe reactor 34. The reactor 34 also includes an outlet 244 formed in thewall 236 to which is conducted an outlet tunnel 248 which comprises aradio-frequency wave guide below cutoff. The system may also include aninert gas source as well as an effluent handling system as shown in FIG.3, although for simplicity such are not shown in FIG. 8.

The conveyor system or waste transport system 204 includes an electricmotor 250 controlled by signals carried on a cable 252 from the control208. The motor 250 drives an input drum 252 of the conveyor system whichin turn drive a conveyor belt 254. An output drum 256 also engages thebelt 254 in a conventional fashion.

Pressure vessels 260 of the type which may best be seen in FIGS. 10,11A, and 11B, are carried by the conveyor belt 254 through the inlettunnel 240 into the radio-frequency reactor 34. The pressure vessels 260are substantially cylindrical in shape and include an inlet 262terminating in a flange assembly 264 which receives a closure cap 266.The closure cap 266 seats against an O-ring or gasket 268 for a gastight seal therewith. The O-ring 268 is also trapped against the flange264. The cap 266 is held in compressive engagement with the O-ring by aplurality of bolts 270. The pressure vessel 260 includes a wall 272which may either be completely transparent to radiofrequency radiation,or be deliberately absorbent to heat the wall by the radio-frequencyenergy such that the wall temperature approximates that of the materialbeing heated. Alternatively, the interior portion of the wall of thecontainer may be thermally insulating to achieve the same purpose. Thepressure vessel 260 is preferably made using fiberglass reinforced hightemperature epoxies or equivalent plastic material to withstand thetemperatures and pressures needed for disinfection. A plurality of wastebags 276 are held in the interior 278 of the pressure vessel 260 forheating by the radio-frequency energy as was set forth above.

A plurality of thermocouple openings 280 are provided in an upperportion of the vessel so that, if desired, temperature readings may bemade of the interior of the vessel 260 to assure a minimum of 90° C. Apair of pressure relief valves 282 are also included. The pressurerelief valves are rated at about 15 psi, that is, they remain closeduntil the internal pressure of the vessel 260 exceeds the externalpressure by 15 pounds per square inch. This allows vapor to be containedeven if the medical waste 16 is heated above 100° C., the boiling pointof water at atmospheric pressure. It also allows the waste or medicalmaterials to be heated to 120° C. without vaporizing most of the waterwithin the bags. The release valves 282 are provided in order to protectthe operators of the system from overpressure within the pressurevessels 260. Should it be necessary to inject additional water into thepressure vessel 260, a water injection port 288 is provided in the wallof the vessel. A rupture disk 290 is also provided in the vessel 260 toprevent excessive buildup of pressure in the event of failure of thepressure release valves 282. An optional disinfected waste port 292 isprovided as an aid for pushing medical waste from the pressure vessel260 following disinfection with the radio-frequency energy.

The pressure vessel 260 also includes gear cogs 300 arranged around theneck 262 of the inlet of the pressure vessel 260. When the pressurevessel 260 is transported into the radio-frequency heating chamber 34,the drive gear box 304 and mounting assembly 301 are normally below thebottom surface 232 of the reactor 34. To rotate the vessel, the drivegear 304 and the mounting assembly 301 are raised so that the drive gear304 engages the cog 300 to rotate the pressure vessel so that allcontainerized medical waste within the pressure vessel 260 is exposed toall three time-varying vectors of the electromagnetic field to furtherensure complete electric field exposure and uniform heating.

In an alternative embodiment the pressure relief valves can be set torelieve the pressure at nearly atmospheric levels. The pressure vesselthus can be used both as a waste bag container for transportationthrough the system and to contain vapors for vapor transfer forcondensation on dry materials.

In the event that the heating is to be taken above the vaporizationpoint at atmospheric pressure, then it is important that the largepressure vessel also be rotated to eliminate the possibility of shadedareas, as previously discussed. Thus, by this method, all parts of thewaste material are exposed to substantial levels of electric fields witha resultant possibility of achieving lower temperature disinfection bythe combined or collateral effects of temperature and electric fields.In practice, the material in the temperature vessel first is heated tothe vaporization point of water as in the case for the system shown inFIG. 3. The dry, relatively poorly absorbing material receives watervapor from the moist medical material and thereby becomes more absorbingto realize an almost equal temperature rise of the wet and dry medicalmaterial within the bags. At this point a minimum temperature in thebags of 90° C. may be realized. Then the bags and the boxes are removedthrough the exit tunnel and heat soaking arrangement as previouslydescribed for the 90° C. or more heat soaking system, except that theheat soaking temperature in this case of 100° C. may be preferred.

Alternatively, it may be desirable to further heat the material atatmospheric pressure to temperatures of about 100° C. or 120° C. Thismay be done by further application of the time varying electric fieldssuch that the material is dehydrated nearly completely and a minimumtemperature of 100° C. or 120° C. is realized through dielectricheating.

In many cases, especially if pressurization at near atmospheric levelsis employed and if heating beyond the vaporization temperature of thedry medical material is required, the total energy or "dose" applied tothe medical waste must be controlled. Energy should be sufficient toaccomplish the desired final temperature with some additional safetymargin. This may result in some of the medical material being overheatedbeyond the desired final temperature of approximately 120° C. However,too little energy can result in underheating some portions of themedical material and too much energy can result in excessive energyconsumption along with partial or complete pyrolysis of the medicalwaste. Excessive waste also generates noxious gases and thereby burdensthe effluent treatment system.

To mitigate these problems, as shown in FIG. 8 sensors 237a and 238b areused to determine the moisture content and/or the presence of sharps.Previously the material may have been weighed and the weight datasupplied to the control unit 208 via a cable 239. The control unit 208then programs the exposure level and controls this via the electricfield sensor 234 and the duration of the exposure by sequentiallyactivating the belt 254 via a line 252 and a motor 250. A sensor 237dremotely monitors the temperature of the material in the vessel 260 bymonitoring the infrared or longer wavelength electromagnetic emissionsfrom the material being heated. The sensor 237e monitors the gaseouseffluent so as to limit excessive pyrolysis.

Additional wall insulation and/or wall heating may also be employed tosuppress heat losses due to convection and diffusion. This is especiallydesirable if heating above the vaporization temperature is needed.Additional wall and panel insulation 241 along with a wall and a panelheater 343 may be employed. The wall and panel heater 343 is alsocontrolled by the control system 208.

For those cases where heating above the vaporization point of water isemployed, it is especially important that the chamber be filled with aninert gas such as nitrogen. The means for the injecting the nitrogen inand keeping the oxygen out are described for the system shown in FIG. 3.For the semicontinuous system shown in FIG. 8, less care is needed incontrolling the direction of sweep gases. However, if a continuousversion of FIG. 8 is employed, the direction of sweep gases should befrom the cooler material to the hotter material as discussed in theembodiment shown in FIG. 3.

The pressure vessel may then be carried, after treatment by theradio-frequency energy, to the outlet tunnel 248 where electricalresistance heaters 306 provide heat soaking to the pressure vessel 260,holding it at the desired temperature for a specified period of time inorder to provide extra assurance of the destruction of pathogens in theinfectious medical waste.

Details of a radio-frequency feed structure for the cavity resonator 32may best be seen in FIGS. 6A, 6B and 6C. The cavity resonator 32 may inan alternative embodiment be fed from opposite sides by loop-typeexciters 310 and 312. The loop exciter 310 is driven at a frequency of40.68 megahertz while the loop exciter 312 is driven at twice thatfrequency, 81.36 megahertz. It may be appreciated that this arrangementallows a highly uniform average power to be present within the cavity.As may best be seen in FIG. 7A, a cavity having standing waves inducedtherein at the lowest mode, has an average power density with a peak atthe center of the cavity. If the cavity is driven at a frequency of81.36 megahertz a pair of power peaks occur, as may be seen in FIG. 7B.The continued effect of the two feeds of the twin feed cavity shown inFIGS. 6A through 6C is shown in FIG. 7C with the power density curve fora relative amplitude for power of 0.864 at the fundamental 40.68megahertz frequency and a relative amplitude of 0.48 at the first octaveor 81.36 megahertz frequency, thereby providing a highly uniform poweracross three quarters of the distance across the cavity as shown in FIG.7C. This further provides uniform heating for the medical waste 16within the cavity.

A detailed flow chart of the process steps carried out by the apparatusand method of the present invention is shown in FIG. 9. In step 400, themedical waste is received at a receiving bay and transferred to a beltconveyor in step 402. Optionally, in step 404, the medical waste 16 maybe appropriately identified by bar coding or any other identificationmethod and may be sorted according to containerized waste intolightweight boxes in step 406, heavy and liquid waste boxes in step 408,sharps containers in step 410 and possibly cardboard in step 412.Optionally, the medical waste may be repacked in processing containerssuch as additional boxes of corrugated material in step 414 and then isfurther transferred by conveyor to a radio-frequency heating system instep 416. The medical waste may be restacked and optional temperaturevalidation procedures may be carried out in step 418.

The medical waste is then segregated in step 420. Disinfected sharpscontainers are fed to a shredder for sharps containers in step 422.Other material is fed to a shredder for general waste in step 424. Thewaste may be optionally separated in step 426.

Preliminary to the use of the present invention, medical waste arrivesat a processing and recycling facility. Preferably the material isshipped in sealed containers, usually sealed plastic bags. The plasticof the bags does not significantly absorb the radio-frequency energywith which the medical waste is treated. This means of shipping medicalmaterials is known in the art and has the advantage that the medicalwaste does not infect or contaminate its handlers in transit.

The containers remain in the heating chamber and receive radio-frequencywaves for a sufficient time to raise the temperature of the medicalmaterials to approximately 85° C. to 125° C. It will be recognized bythose skilled in the art that temperatures as high as 170° C. may beemployed without adversely affecting the material to be disinfected. Inthe disclosed embodiment, the medical waste 16 is moved through theradio-frequency treatment unit 12. The total dose of radio-frequencyenergy to which the medical waste 16 is exposed during its dwell time inthe unit 12 is planned to provide sufficient disinfection.

Preferably, a medical material disinfection facility using the presentinvention is validated to assure the adequacy of the disinfectionprocess. Validation may be performed when each facility is constructedand at intervals during its operation. Validation may consist of placingheat detecting devices such as thermocouples, resistance temperaturedetectors, or the like, and/or known amounts of particularmicroorganisms which are resistant to heat into a load of medicalmaterials. Sufficient radio-frequency energy is applied to raise thetemperature of a load to about 85° C. to 125° C. If thermocouples areused, they should all record at least 85° C. indicating that allportions of the load have been heated to at least 85° C. and that thereare no cold spots where microorganisms might survive. After the entiredisinfection cycle is complete, the microorganism samples are removedfrom the container and cultured by being given nutrients and otherappropriate conditions for growth in order to determine whether any havesurvived the radio-frequency energy treatment. A typical heat resistantmicroorganism which may be used in validation of the disinfectionprocess is Bacillus stearothermophilus. If more than one in ten thousandof any microorganism survives the exposure to radio-frequency energy,the exposure must be increased and another container tested, and thepreviously tested container must be retreated with radio-frequencyenergy. On retest, a temperature of 92° C. may be tried. If that is notadequate, further retests at 94° C., 96° C., and 98° C. may beundertaken until the necessary kill rate is obtained.

The containers are held in the radio-frequency chamber and exposed toradio-frequency waves for a sufficient time to raise the temperature ofthe medical materials to at least approximately 85° C. It will berecognized by those skilled in the art that temperatures as high as 170°C. will not adversely affect the process. Preferably, the exposure timeto radio-frequency waves will vary depending upon the radio-frequencypower and the weight of material in order to elevate the temperature ofthe medical materials to 85° C. to 125° C. and hold that temperature forup to 45 minutes as an extra margin of safety, assuring an even higherkill rate. However, the optimal exposure time to the radio-frequencywaves and the field strength of the electromagnetic field of thetime-varying field for a particular facility will vary and may bedetermined as described above.

In a still further embodiment, the load may consist of 18 inch by 18inch boxes loaded with polyethylene bags filled with hospital wastecontaining approximately 5 to 10 percent water by weight. In a furtherembodiment the load may consist of 18"×18" boxes loaded withpolyethylene bags filled with shredded hospital waste. Inside each suchbox an envelope containing test strips loaded with 1×106 spores ofBacillus subtilis, var. niger. may be employed. Thermocouple temperatureprobes also may be placed within and around the boxes.

Another embodiment of the invention consists of starting with medical orveterinary waste that has been presorted into containers of plastic andgeneral medical waste, respectively. High grade plastics are employed inmedical products and can be shredded and molded into a variety of otherproducts. This waste is subjected to radio-frequency energy and thecontainers of disinfected waste are moved to a shredder for theplastics. For example, an electrically powered shredder having apneumatic ram assist with a negative pressure canopy can shred themedical waste to small particles. Such a shredder may be purchased fromShredding Systems, Inc. of Wilsonville, Oreg., and is identified as amodel Dual 1000 E. The negative pressure air canopy removes odors andparticles entering the surrounding air and contaminating the atmosphere.The odorous air is then scrubbed and particulates removed by impactfilters or electromatic precipitators. The containers or medical wastebags are opened and the disinfected plastic is placed in the shredderand shredded to particles of about one-quarter to one-half inch meanlinear dimension. The disinfected shredded plastic is transferred to 55gallon drums for shipment to plastic recyclers.

Likewise, the containers of disinfected general medical waste may beplaced in a general medical waste shredder. After the containers areopened, the disinfected general medical waste is placed in the shredderand shredded to particles have a mean linear dimension of one-quarter toone-half inch. The disinfected waste is placed in further containerscontaining a mixture of paper, plastic, and metal, which can be used asfuel. Possible users include cement kilns which burn fuel to createtemperatures of about 130° C. or more and which might otherwise employhigh sulfur coal. Because the general medical waste is low in sulfur,its use as fuel will not generate sulfur compounds which might bereleased into the atmosphere and contribute to acid rain.

It is believed that part of the superior effectiveness of theradio-frequency heating method disclosed herein is due to the fact thatradio-frequency electromagnetic energy penetrates large boxes andvolumetrically heats the contents thereof very efficiently. However,this factor alone is not believed to account entirely for the differenceobserved. It is further believed that the efficacious results of theinstant process may be due to the fact that bacteria and viruses have amuch higher water content than most of the mixed medical waste. As aresult, the relatively high dielectric constant of the bacteria andviruses efficiently couples the electromagnetic or time-varyingelectromagnetic field energy to the water, causing rapid heating of themicroorganisms and subsequent inactivation or destruction thereof.Substances with high dielectric constants selectively absorbradio-frequency energy. Therefore, radio-frequency energy may heat thebacteria and viruses to a lethal temperature before the surroundingwaste reaches what is generally considered a lethal temperature.

Individually, the boxes were placed in a two-plate 40 KW radio-frequencyheating chamber. The radio-frequency was 18 megahertz. The followingparameters were used:

    ______________________________________                                        Plate KV     =       13 KVDC                                                  Plate Amps   =       0.5 Amps (No Load) to                                                         0.8 Amps (Loaded)                                        Grid Amps    =       0.4-0.6 Amps                                             Electrode Height                                                                           =       9.75" (Approximately                                                          1" above box)                                            Time         =       57 Minutes                                               Temperature  =       108° C. (maximum internal)                        ______________________________________                                    

At the end of the run, the load was allowed to cool. The boxes andindividual bags were opened and the spore strips were removed andcultured according to standard techniques. For one run, of thirteenstrips, four showed no growth at all. For the nine viable strips, theD-value, or amount of time needed to kill 90% of a test dose, wascalculated. For RF, at a maximum temperature of 108° C., the D-value wasapproximately 9 minutes.

As a control, a dry heat test vessel was used to determine the D-valuesfor Bacillus subtilis, var. niger spore strips at 149° C., 160° C., and179° C. These D-values were graphed and extrapolated to 108° C. At atemperature of 108° C. the D-value for the dry heat process was 20minutes. Therefore, at a temperature of 108° C. the D-value of 9 minutesfor the RF treatment was less than half of the dry heat value. This isevidence that RF heating is markedly more efficient than is the dry heatprocess, in that it yields a comparable microbial kill rate insignificantly shorter time.

At 121° C., the D-value for the RF heating process was 0.31 minutes. Acontrol test of dry heat yielded no kill at this time at anytemperature. At 121° C., RF was markedly more effective than the dryheat process.

In a still further alternative embodiment of the present invention, anapparatus 600 for treatment of medical materials, the apparatus 600 asmay best be seen in FIG. 15, comprises a comminuter 602 for receivingthe waste material 16 from a source of waste. The comminuter receivesthe containerized waste 16 and transfers it to a water station 604 wherewater may be added to broken up waste. A compactor 606 is connected tothe water station 604 to squeeze or increase the density of the waste tobe treated. A radio-frequency treatment apparatus 608, which may eitherbe of the parallel plate type or resonant cavity type, as disclosedhereinabove, receives the compacted waste and heats it to a temperaturebetween 85° C. and 125° C. to disinfect the waste. The treated wastethen leaves the radio-frequency treatment apparatus.

In further detail, as may best be seen in FIG. 16, the medical waste isreceived in a step 620, the waste is then sent to the comminuter 602wherein step 622 it is broken into an average particle size ofapproximately 1 to 2 inches linear dimension. The comminuter 602 maycomprise a shredder of the type previously disclosed. The waste is thenexamined to determine whether water needs to be added in a step 624. Ifwater is to be added, the waste is further examined in a step 626 todetermine whether it is desirable to add an aqueous foam, such as asurfactant and water. In the event that foam needs to be added, it isadded in a step 628 in water station 604. If foam need not be added,water is added in a step 630. The material having the additional watereither in the form of foam or pure water, is then examined to determinewhether the waste is dense enough. Likewise, waste which is not too drywhich is adequately wetted is also examined. If it is considered not tobe dense enough, the waste is compacted in a step 634 in the compactor606 to achieve a higher desired density. The proper density waste 16then, as shown in FIG. 14, is placed in a closed container 635 having abody 635a and a top 635b fitted to the body 635a which may be comprisedof an epoxy filled with fiberglass which closed container may either beable to maintain pressure slightly above atmospheric or up to 15 poundsper square inch above atmospheric pressure. The container is then placedin the radio-frequency treatment apparatus which may either be aparallel plate type or resonant cavity in which should be excitedbetween 10 megahertz and 100 megahertz. If the waste container 635 isnot rated at a pressure of 15 pounds per square inch above atmosphericpressure, the radio-frequency treatment apparatus itself may bepressurized so that the waste may be adequately heated therein. When theelectric field is applied to the waste 16 by the radio-frequencytreatment apparatus 608 in the step 638 waste 16 having water thereon ortherein is rapidly heated liberating vapor which travels to portions ofthe waste which do not have water thereon. The water vapor thencondenses on the dry portions of the waste 16, having been confined inproximity with the drier waste by the closed container. The water vaportransfers its heat of vaporization to the previously dry waste andincreases its radio-frequency energy absorption. The waste is thenadditionally heated by transfer of energy from the radio-frequencyelectric field which heats the condensed water within or on thepreviously dry waste. In the event that the container 635 can withstanda pressure over atmospheric, the waste may be heated to above 100° C.preferably to 100-125° C. If the radio-frequency treatment apparatus andcontainer are only able to maintain the waste 16 at atmosphericpressure, the waste will be heat to 90° C.-100° C.

One of the advantages of the instant process is that when the waste 16is comminuted, dielectric materials in the waste 16 are brought intoclose contact with the metal-containing portions of the waste therebyreducing the likelihood of arcing. In addition, arcing is reduced by theaddition of the foam or water which would tend to quench the arc and inaddition prevent combustible materials in the waste from burning shouldarcing occur when the radio-frequency electric field is applied. Theclosed container 635 also helps to prevent unwanted combustion of thewaste 16 while it is being heated by the radio-frequency electric fieldsince the amount of oxygen within the container is limited and would berapidly used when combustion starts. The container itself, being made ofa combination of epoxy and fiberglass, can withstand temperatures of upto 400° F. before being damaged by the heated. Thus, the container issubstantially combustion resistant.

In order to render the process more efficient, the aqueous foam may beadded in the step 628 which provides an absorbing dielectric in contactwith metal portions of the comminuted waste to prevent combustion due toarcing but which reflects relatively little radio-frequency energydirected into the waste. This is due to the fact that such a foamaqueous dieelectric typically has a dieelectric constant of 2 whichwould result in a reflection of only about 10% of the power directed atthe waste 16. While liquid water, having a dieelectric constant of 80would reflect almost 90% of the radio-frequency power fed to comminutedwaste.

The process is also further rendered efficient by the use of thecompaction step 634 which allows more waste to be processed within theradio-frequency treatment apparatus in a selected period of time. It maybe appreciated, however, that the compaction could not occur to anyindefinite degree as the amount of material to be heated may be soincreased that the time in which heating takes place might besignificantly slowed. In any event, compaction of the waste from 5 or 10pounds per cubic foot, which is the density of the waste as it isreceived from hospitals and the like, to a density of 25 to 30 lbs. percubic foot would not significantly effect the heating time.

The foregoing descriptions of the preferred embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously many othermodifications and variations are possible in light of the aforementionedteachings. The embodiments were chosen and described to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to utilize best the invention in itsvarious embodiments and with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of disinfecting and processingdielectrically heterogeneous bulk medical waste to inactivate pathogens,comprising the steps of:comminuting the dielectrically heterogeneousmedical waste into comminuted dielectrically heterogeneous medical wasteparticles having a predetermined size; placing the comminuteddielectrically heterogeneous medical waste particles in a bulkdielectric processing container; conveying the bulk dielectricprocessing container with the comminuted dielectrically heterogeneousmedical waste particles therein through an Opening and into a treatmentregion of a treatment chamber; and applying within the treatment regiona transverse mode radio-frequency electric field from a pair of parallelplates, the transverse mode radio frequency electric field having afrequency in the range of about 3 megahertz to about 80 megahertz, thetransverse mode radio frequency electric field heating the comminuteddielectrically heterogeneous medical waste particles to a temperature of85° C. to 125° C., the transverse mode radio-frequency electric fieldsubstantially penetrating the comminuted dielectrically heterogeneousbulk medical waste particles and exhibiting a square of the electricfield strength that varies by no more than a factor of two in thetreatment region to produce disinfected comminuted dielectricallyheterogeneous medical waste particles without substantially producingionized gas.
 2. A method of disinfecting and processing dielectricallyheterogeneous bulk medical waste to inactivate pathogens according toclaim 1, wherein the step of comminuting the dielectricallyheterogeneous bulk medical waste comprises reducing the dielectricallyheterogeneous bulk medical waste to comminuted dielectricallyheterogeneous bulk medical waste particles in a size range of 0.25 to0.50 inch.
 3. A method of disinfecting and processing dielectricallyheterogeneous medical waste to inactivate pathogens according to claim1, wherein the step of applying the transverse mode radio-frequencyelectric field lasts for a duration of at least approximately 5 minutes.4. A method of disinfecting and processing dielectrically heterogeneousmedical waste to inactivate pathogens according to claim 1, wherein thestep of applying the transverse mode radio-frequency electric fieldlasts for a duration of between 3 and 30 minutes.
 5. A method ofdisinfecting and processing dielectrically heterogeneous medical wasteto inactivate pathogens according to claim 1, further comprising, thestep of sorting the dielectrically heterogeneous medical waste intoplastics waste and general medical waste and placing the plastics wasteand general medical waste into separate processing containers forplastics waste and general medical waste, respectively.
 6. A method ofdisinfecting and processing dielectrically heterogeneous medical wasteto inactivate pathogens according to claim 5, further comprisingrecycling the sorted medical waste by reusing the disinfected plasticwaste and using the disinfected general medical waste as fuel.
 7. Amethod of disinfecting and processing dielectrically heterogeneousmedical waste to inactivate pathogens comprising the stepsof:comminuting the dielectrically heterogeneous bulk medical waste intocomminuted dielectrically heterogeneous medical waste particles having apredetermined size; placing one of the comminuted dielectricallyheterogeneous medical waste particle types in a bulk dielectricprocessing container; adding water to the dielectrically heterogeneouscomminuted medical waste particles; conveying the bulk dielectricprocessing container with the comminuted dielectrically heterogeneousmedical waste particles therein through an opening and into a treatmentchamber; and applying within the treatment chamber for about fiveminutes a transverse mode radio-frequency electric field from a pair ofparallel plates, the transverse mode radio-frequency electric fieldhaving a frequency in the range of about 3 megahertz to about 80megahertz, the transverse mode radio-frequency electric field heatingthe comminuted dielectrically heterogeneous medical waste particles to atemperature of about 85° C. to about 125° C., the transverse moderadio-frequency electric field substantially penetrating the comminuteddielectrically heterogeneous bulk medical waste particles anddisinfecting the comminuted dielectrically heterogeneous medical wasteparticles without substantially producing ionized gas.
 8. A method ofdisinfecting and processing dielectrically heterogeneous medical wasteto inactivate pathogens according to claim 7, wherein the step of addingwater further comprises adding a foam comprising water and a surfactantto the dielectrically heterogeneous comminuted medical waste particles.9. A method of disinfecting and processing dielectrically heterogeneousmedical waste to inactivate pathogens according to claim 7, furthercomprising the step of compacting the comminuted dielectricallyheterogeneous medical waste particles.
 10. A method of disinfecting andprocessing dielectrically heterogeneous medical waste to inactivatepathogens according to claim 7, further comprising the step ofseparating the dielectrically heterogeneous medical waste into materialcomprising plastic and refuse-derived fuel.